In the fuse links which are available on the market, the solder substance is usually a tin-cadmium alloy. SnCd 80 20, i.e. an alloy comprising 80% by weight of tin and 20% by weight of cadmium, is customary. Recently, however, there has been a desire to avoid cadmium, for reasons of environmental protection. There are fuse links on the market in which the fusible conductors include a solder substance comprising SnBi 95 5. In these, the fusing times of the fusible conductors provided with this solder are subject to a considerably wider scatter than those which use the conventional SnCd solders.
SnBi solders generally tend to flow. To prevent this, in a fuse link which is commercially available, the solder has been covered with a layer which contains silicone. In this case, the arcing performance of the fuse link may deteriorate considerably when the silicone breaks down, on account of the carbon atoms.
The fusible conductor and solder system is generally to be configured in such a way that in the event of prolonged overload currents the solder melts locally, dissolves the material of its support, i.e. the fusible conductor and thereby accelerates switching off. In this context, one generally refers to a M effect. The solder should satisfy the following conditions:                Sufficient solubility of the solder substance with regard to the fusible conductor material, generally copper,        no flow of the solder during fusing,        solder bridges between the ends of the fused fusible conductor should be avoided.        
An organic coating has already been provided as a solder stopping agent which is intended to prevent the solder from flowing in the event of a solder substance which does not include cadmium. Although it is in this way possible to prevent solder substances without cadmium from flowing, the thermal decomposition of the organic matrix during fusing of the fusible conductor, i.e. in order to break the fuse, may lead to the formation of an electrically conductive plastic film, which may prevent the circuit from being broken.
The problem of flow has existed since the start of attempts to use cadmium-free solders.